Herman Poole Blount, an Alabamian, takes on the identity of Sun Ra: an interstellar prophet who, with conviction, says he’s from Saturn, not Alabama.
Daniel Dumile takes the moniker Zev Love X in the group KMD, retreats from the hip hop scene, and comes back with a new identity: MF Doom.
Johannes Brahms makes drastic changes to his 1854 Piano Trio in B major as his works are being republished in 1889. In the first movement, he takes out the violin flourishes in the opening melody that his 21 year old self found appropriate. It is the only piece out of what is being republished that he edits.
Bob Dylan, traditionally acoustic, plays electric at the 1965 Newport Folk Festival and is criticized for going against his folk roots.
Authenticity is about being of an undisputed origin; to know what something is for good. A rock is authentic. Musicians on the other hand change their identity, their music, their band, and other parts of themselves constantly.
Why do we have to worry about authenticity in music if music itself necessitates the flux?